gRPC

The server includes a gRPC client that fetches assessment algorithm bundles from the Go diagnostics backend. This data powers the adaptive algorithm in student assessments.

BundleFetcher Trait

Pluggable interface for bundle sources:

#[async_trait]
pub trait BundleFetcher: Send + Sync + 'static {
    async fn fetch(
        &self,
        network_index: i32,
        curriculum_index: i32,
    ) -> Result<Vec<u8>, BundleFetchError>;
}

GrpcBundleFetcher

Production implementation connecting to the Go diagnostics service:

pub struct GrpcBundleFetcher {
    endpoint: String, // e.g. "http://diagnostics:50051"
}

Uses hand-written proto types (no protoc/build.rs required):

// Request
pub struct GetAlgorithmBundleRequest {
    pub network_index: i32,
    pub curriculum_index: i32,
}

// Response
pub struct GetAlgorithmBundleResponse {
    pub data: Vec<u8>,  // JSON-encoded AlgorithmBundle
}

The hand-written tonic client matches the Go server’s service definition:

impl GrpcBundleFetcher {
    pub async fn fetch(&self, network_index: i32, curriculum_index: i32)
        -> Result<Vec<u8>, BundleFetchError>
    {
        let mut client = DiagnosticsClient::connect(self.endpoint.clone()).await?;
        let response = client.get_algorithm_bundle(GetAlgorithmBundleRequest {
            network_index,
            curriculum_index,
        }).await?;
        Ok(response.into_inner().data)
    }
}

NoopBundleFetcher

Development fallback when the Go backend is unavailable:

pub struct NoopBundleFetcher;

impl BundleFetcher for NoopBundleFetcher {
    async fn fetch(&self, _, _) -> Result<Vec<u8>, BundleFetchError> {
        Err(BundleFetchError::Transport("noop fetcher".into()))
    }
}

Used when DIAGNOSTICS_GRPC_URL is not set.

Error Types

pub enum BundleFetchError {
    Transport(String),
    Status(tonic::Status),
}

Data Flow

graph LR
    GQL[GraphQL Mutation] -->|refreshAssessmentBundle| Fetcher[GrpcBundleFetcher]
    Fetcher -->|gRPC| Go[Go Diagnostics :50051]
    Go --> Fetcher
    Fetcher --> Repo[AssessmentBundleRepository]
    Repo --> PG[(PostgreSQL)]
    PG -->|assessmentBundle query| Client[Rust Client]
    Client -->|AlgorithmBundle::into_engine| Engine[AlgorithmEngine]

1. Refresh — GraphQL mutation triggers gRPC fetch from diagnostics service
2. Store — Response bytes (JSON AlgorithmBundle) are upserted into PostgreSQL
3. Load — Client queries the bundle via GraphQL
4. Build — AlgorithmBundle::from_json() → into_engine() builds the AlgorithmEngine

Related

• Algorithm — how the engine uses bundle data
• Bundles — AssessmentBundleRepository storage
• GraphQL — mutations that trigger fetches
• Overview — server architecture